添加0139.单词拆分 Python DP剪枝方法

problems/0139.单词拆分.md

@@ -394,7 +394,28 @@ class Solution:
                     dp[j] = dp[j] or (dp[j - len(word)] and word == s[j - len(word):j])
         return dp[len(s)]
 ```
+DP（剪枝）
 
+```python
+class Solution(object):
+    def wordBreak(self, s, wordDict):
+
+        # 先对单词按长度排序
+        wordDict.sort(key=lambda x: len(x))
+        n = len(s)
+        dp = [False] * (n + 1)
+        dp[0] = True
+        # 遍历背包
+        for i in range(1, n + 1):
+            # 遍历单词
+            for word in wordDict:
+                # 简单的 “剪枝”
+                if len(word) > i:
+                    break
+                dp[i] = dp[i] or (dp[i - len(word)] and s[i - len(word): i] == word)
+        return dp[-1]
+
+```
 
 
 ### Go：